Weird loss of power issue

[Gcoder99]

Ok, so I'm having a strange issue where my 1997 Explorer 4.0L starts, idles, and runs fine, but after about 20 minutes of driving, it completely loses power and starts misfiring. It'll throw a code for the misfire and running too lean, and in pending codes, it says "P1131 Lack Of HO2S Switch – Sensor Indicates Lean". I replaced all of the O2 sensors, and the issue still persists but now it's not giving any codes. Also earlier this month, the fuel pump gave out, so I replaced that, but under live data on my scan tool, it says "fuelsys1---cl fault." I'm pretty lost lol, Fuel pump? O2 sensors? Vacuum lines? Any ideas?

 

[410Fortune]

Check your fuel pressure
Sounds like something fishy with either your new fuel pump or?
Check your battery terminals they should be clean and tight

What brand fuel pump did you use? Did you replace the filter as well?
I would check fuel pressure first just to rule it out

The codes are likely from when it is dying and running out of fuel ?

 

[amj441]

Did you check the tank while you had it out? could be alot of dirt at the bottom of the tank that falls off and gets sucked back up over time onto the pickup sock.

I had the whole old sock floating around in my tank

 

[1sicbronconut]

Check your fuel pressure
Sounds like something fishy with either your new fuel pump or?
Check your battery terminals they should be clean and tight

What brand fuel pump did you use? Did you replace the filter as well?
I would check fuel pressure first just to rule it out

The codes are likely from when it is dying and running out of fuel ?

This!! a lot of non-ford fuel pumps are 100% junk.

 

[J_C]

Ok, so I'm having a strange issue where my 1997 Explorer 4.0L starts, idles, and runs fine, but after about 20 minutes of driving, it completely loses power and starts misfiring. It'll throw a code for the misfire and running too lean, and in pending codes, it says "P1131 Lack Of HO2S Switch – Sensor Indicates Lean". I replaced all of the O2 sensors, and the issue still persists but now it's not giving any codes. Also earlier this month, the fuel pump gave out, so I replaced that, but under live data on my scan tool, it says "fuelsys1---cl fault." I'm pretty lost lol, Fuel pump? O2 sensors? Vacuum lines? Any ideas?

fuelsys1 cl fault makes me wonder if you have an intake manifold leak, but as others mentioned, I'd check fuel pressure just to rule that out.

What are your long term fuel trims on bank 1 and 2, now and when the fault happens?

 

[C420sailor]

CL fault sounds to me like it is having trouble going into closed loop.

initially it runs in open loop…then somewhat quickly it should go into closed.

You need to monitor or log your live data to see what is happening when the problems start.

To me, it sounds like the truck is running well in OL with the fixed fuel tables, then goes to hell when it tries referencing sensors.

I’d check MAF, IAT, TPS, the O2 sensors (and associated fuses), ECT (engine coolant temp sensor for PCM, not cluster), etc. Anything that feeds data to the PCM for the injector tables and such.

My parents Expedition had a similar issue that coincided with the EGR valve opening (I think) so give your EGR valve and plumbing and DPFE sensor and hoses a good look over too. They had a pretty massive exhaust manifold rot problem.

As 410fortune mentioned, check fuel pressure for good measure.

Also…do you have any major exhaust leaks at or upstream of the sensors? That can really mess with oxygen sensors.

 

[Gcoder99]

Thank you guys. I'm going to test my fuel pressure. Either I'm super unlucky or my car is killing fuel pumps because this is its 3rd fuel pump lol. The other two just died outright, though, so I don't know; maybe it's that. I'll look over all the other stuff too and record my live data and get back to you guys --Thanks again.

Yes I replaced the fuel filter
I dont know what brand of fuel pump I got it at Autozone but its not duralast
The tank looked great inside which honestly surprised me
Not sure on the fuel trim, exhaust/intake manifold leak, or EGR ill take a good look at all of those
Its only throwing codes for bank one as of right now (not sure if that rules anything out)

 

[410Fortune]

Must at least check fuel pressure to rule it out

Parts Store fuel pumps don’t always last very long

You have checked all your fuses? There are a couple of fuses for the 02 sensors and their heaters

On live data we want to see that 02 sensor switching or it will never run right. Lack of switching can be two things a bad 02 sensor that is not reading or a sensor that is expected to switch and is not… it is staying lean for example, even through the computer has made changes to the fueling and expected to see switching… this would be a lean or rich condition that was not able to be corrected by the computer

Your 97 is it a sohc engine or ohv 4.0?

P1131 is bank 1 sensor 1 lack of switching indicates lean
The pcm
Has attempted to correct the lean condition on bank 1 and was not able to, the lean condition persists
Usually this means the 02 sensor is working and telling you lean is the issue

It is good to note that a fuel pressure issue usually effects both banks

It is important now that you check fuel psi just to rule it out. Should be around 42 psi

Then you want to watch bank 1
Sensor 1 On the live data and see if it’s
Voltage fluctuates or matches what is shown for bank 2 sensor 1.

Could be air Leaks or exhaust leaks, could be a bad injector

The pcm is telling us where to look

 

[amj441]

(the 97 sohc does have a return type fuel line, perhaps the fuel pressure regulator is leaking?

 

[410Fortune]

If a fuel pressure regulator is bad you will have raw fuel in the vacuum line to it

Fuel Psi should be 42 psi at the rail

 

[Gcoder99]

Well, as it turns out, it was indeed a fuel pressure issue. Someone kindly put sugar in my gas tank, and somehow I didn't notice. I can't think of anyone that I pissed off lol, but I guess now's a good time to buy a locking gas cap. I thoroughly cleaned out the tank and fuel lines and replaced the destroyed fuel filter and pump. She runs like a dream now. I also threw some injector cleaner in there just because. Anyway, I appreciate all the help, guys, and pointing me in the right direction. Stay safe out there

 

[410Fortune]

Wow that is the big suck!!
Locking gas cap for sure

Glad you got it sorted out what a nightmare
Any chance of getting some security cameras on the truck? Maybe in the truck? We run cheapo dash cams that will record even when the truck is locked and it is bumped or
Messed with

 

[C420sailor]

People are such *******. Can’t be man enough to square up, so they pull 10-ply **** like that.

Glad you got it sorted. Hoping you figure out who did it and beat them half to death.